1. Field of the Invention
This invention is in the field of aromatic polyamide or aromatic copolyamide filaments or yarns and the adhesion of such filaments or yarns to rubber, elastomer or resin.
2. Description of the Related Art
Para-aramid fibers are widely used as a structural reinforcement in tires and mechanical rubber goods. A coating is frequently applied to the fiber to assist the adhesion of the rubber or elastomer to the fiber. Such coatings are normally based on epoxy or isocyanate type resins or various resorcinol-formaldehyde latex (RFL) mixtures. The widely used RFL adhesion system requires a two step process. In some embodiments, the coating material is an epoxy resin subcoat and a resorcinol-formaldehyde topcoat. Chemical bonding to rubber occurs via double bonds that are introduced onto the fiber surface. The double bonds serve as rubber-cure sites that eventually co-cure into the rubber matrix.
U.S. Pat. No. 2,128,635 describes the RFL process. U.S. Pat. No. 3,307,966 describes the use of a phenol blocked isocyanate-epoxy coating for a pre-dip formulation.
For industrial hygiene reasons, there is a requirement to reduce, and preferably eliminate, the use of both resorcinol and formaldehyde in rubber goods manufacturing. There is, therefore, a need to find alternative environmentally friendly adhesion promotion compounds to enhance the effectiveness of the bond strength between the fiber and the rubber, preferably by a one step process. Examples of rubber goods where such a process can be used is in the manufacture of power transmission belts, conveyor belts, tires and hoses. Another field of use is in fiber reinforced composites where appropriate fiber treatment can reduce delamination within the layers of the composite.